This is a PA view of the heart, with left atrium unroofed to show the mitral valve.

The aortic root and mitral annulus are connected by a fibrous lamina of varying thickness and length (light blue highlight marks approximate extent behind left atrial wall). Variously called "subaortic curtain" or "intervalvular fibrosa" by anatomists, it is an important component of the cardioskeleton.

(Reproduced courtesy of Xiang-Ning Li MD, Department of Anesthesiology, University of Washington.)

Normal Intervalvular Fibrosa

In this transesophageal echo view, one can see the tissue membrane (arrow) interposed between the aortic root and the anterior mitral leaflet.

(Reproduced courtesy of Xiang-Ning Li MD, Department of Anesthesiology, University of Washington.)

The intervalvular fibrosa is a thin, tough but flexible barrier composed of endocardium on the blood side, a variable thickness of dense collagen, and epicardial fat and serosa on the outer side. Diseases which affect the aortic valve and the mitral valve may also affect the intervalvular fibrosa, e.g. senile calcific sclerosis and bacterial endocarditis. It is uncommon for such involvement to become clinically significant unless valve repair is hindered by thick calcium deposits in the fibrosa or degeneration of its supporting function and resultant valve regurgitation.

This echo image features a patient with progressive aortic and mitral regurgitation after receiving a tissue valve for acute aortic endocarditis. The echo demonstrates formation of a very large (>10 cm) aneurysmal lumen interposed between the aortic root and the left atrium, which is compressed. Deformation of the anterior mitral leaflet prevents adequate valve closure leading to regurgitation. During diastole, reflux of blood pumped into the pseudoaneurysm gives rise to a regurgitant jet mimicking aortic regurgitation. The aortic valve itself was largely competent.

(Reproduced courtesy of Donald Oxorn MD, Department of Anesthesiology, University of Washington.)

Sketch of Intervalvular Fibrosa Aneurysm

Over time, the corrupted intervalvular fibrosa expanded to form a thin walled pseudoaneurysm, eventually compressing the left atrium and burgeoning outwards anteriorly and posteriorly about the aortic root to form anterior and posterior sacs joined by a narrow fibrous canal. At the time of operation, the wall of the pseudoaneurysm was extremely thin and translucent in some places. Cardiac rupture was imminent. The goal of repair was to reconstruct the aortic root and install a composite graft anchored to the anterior mitral leaflet. Without the anchoring function of the intervalvular fibrosa, anchoring the graft and achieving a hemostatic seal proved very difficult.